fix(types): consolidate enhancement alias and fix update command

- Add "enhancement" to util.issueTypeAliases for consistency
- Make types.IssueType.Normalize() case-insensitive and include all aliases
- Fix update.go to normalize type before validation
- Remove duplicate type validation block in update.go

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/types/types.go

@@ -529,11 +529,16 @@ func (t IssueType) IsValidWithCustom(customTypes []string) bool {
 }
 
 // Normalize maps issue type aliases to their canonical form.
-// For example, "enhancement" -> "feature".
+// For example, "enhancement" -> "feature", "mr" -> "merge-request".
+// Case-insensitive to match util.NormalizeIssueType behavior.
 func (t IssueType) Normalize() IssueType {
-	switch t {
-	case "enhancement":
+	switch strings.ToLower(string(t)) {
+	case "enhancement", "feat":
 		return TypeFeature
+	case "mr":
+		return TypeMergeRequest
+	case "mol":
+		return TypeMolecule
 	default:
 		return t
 	}

internal/util/strings.go

@@ -4,9 +4,10 @@ import "strings"
 
 // issueTypeAliases maps shorthand type names to canonical types
 var issueTypeAliases = map[string]string{
-	"mr":   "merge-request",
-	"feat": "feature",
-	"mol":  "molecule",
+	"mr":          "merge-request",
+	"feat":        "feature",
+	"mol":         "molecule",
+	"enhancement": "feature",
 }
 
 // NormalizeIssueType expands type aliases to their canonical forms.